Thermal images are used to produce a visual image of a scene in darkness. In such images, articles in the scene which are above ambient temperature can be easily visualised. However, one major difficulty with conventional thermal images is that the images contain little or no depth information, so that it is very difficult to ascertain whether one part of the image is in front of or behind another part of the image. Thus, when a thermal image is taken of a scene which, for example, may contain people, the thermal image will clearly show each of the individual people, but will not provide sufficient information to ascertain the relative positions of the people in space.
In many applications, it is necessary that the image does include depth information so that the image provides sufficient information of the scene to suit a particular purpose.